cooling issues

[dsm95gsxer]

I recently tried a raised pressure cap on my cooling system. It went fine for about 20 miles, then it started to act up (it only cools at idle with the cap off) I replaced my thermostat, took off my radiator, cleaned it out, my compression is 150 across the board and my system will hold 16psi for at least 20 minutes. I'm also not getting any heat from my heater core and I blew through it and it is also not blocked. My water pump is not leaking and has no shaft play. Any thoughts similar problems or diagnosis would be appreciated. I've done some searching and have found nothing similar.

 

[dave99gst]

after its warm and the cap is off can you see the coolant moving ?
fans work ?
ya sure the thermostat isnt upside down?

 

[dsm95gsxer]

I put the thermostat in the way it came out (I put a new one in when I redid my head 3,000 to 4,000 miles ago) The fans will kick on. The only thing I'm not sure about is the coolant moving, if I let it idle it slowly starts to warm up and then it just starts spitting out of the cap opening. My radiator dosen't warm up either. Its starting to sound more and more like a failed water pump.

 

[chubb]

sounds like water pump.. could be thermostat is not opening either....

 

[dsm95gsxer]

It was the water pump, I bought a remanufactured pump at napa and it used plastic blades. The impeller was seperated from the main shaft.